If God has provided the means, surely it is our own fault if we refuse or neglect to use them. (See Note E, p. 156.)

PHYSIOLOGY OF ADVANCED AGE.

The characteristics of age being open to ordinary observation, a popular term-DECAY-is applied to the aggregate. This word has a very wide and deep signification in science. It is the province of physiology to analyse and define it. As a general expression, it is suitable both in science and ordinary language, but it must not exclude a careful attention to the special phenomena it includes.

In order to render this section intelligible to non-professional readers, it is necessary to make a few preliminary remarks.

Physiologists distinguish the textures of the body from the proximate elements, or materials of which they are composed. Flesh, bones, cartilages, membranes, vessels, etc., the skin, the blood, the fluids, nerve matter, etc., these are all made up of a comparatively few materials: albumen, gelatin, fibrin, fat, together with lime

potass, soda, magnesia, iron, chlorine, and oxygen, in various combinations, and a large amount of water,-a compound of oxygen and hydrogen.

It is with these materials that the mysterious principle, life, constructs the textures and builds up all the organs, compacting them into one whole.

While life continues there must be a constant influx into the system of raw materials, as food and air. These undergo in the stomach and lungs changes fitting them to become parts of the living blood and textures.

The reduction of these materials into the form of the proximate elements, and appropriating them to build or repair the various organs, is termed digestion and assimilation. A highly complicated, curious, and beautiful mechanism is provided for the purpose, which is the object of the science of anatomy. Passing by the mechanism, we confine our attention to the materials.

Every active motion of the body and mind involves the use and destruction of some part of the substances composing the blood and tex

tures. After fulfilling these uses they undergo changes, and are finally excluded from the body (excretions). During health there is a normal order, a fixed and regular direction and manner, in all these changes.

We can distinguish two groups of materials, and two series of changes. To one group we apply the term nitrogenous, because the element nitrogen takes the leading part in them. other we designate carbonaceous, from a similar predominance of carbon.

The

The materials containing nitrogen are the nutritive parts of food; those in which carbon prevails, the carbonaceous, are for the maintenance of animal heat, essential to preserve the due temperature for all the actions.

The latter, however, have an intermediary use. They become fat, and this aids the mobility of the muscles, and gives rotundity and beauty of form to the surface.

The nitrogenous matters, when used up, pass out of the system chiefly by the urine.

The carbonaceous are thrown off for the most part in the breath.

In the urine, too, the saline constituents leave

the system.

It can now be partly understood how any interruption of the supply of food, or pure air, and how any disorder, or disturbance of the changes, the metamorphoses of the constituents or proximate elements of the body, produce various diseases.

Let us now contemplate the condition of a person in what would be termed good health, who would, if interrogated, say, "I am quite well," or perhaps, "I am as well as I can expect;" that is, free from any overt disease, but who has reached the age of say 55 to 70, and is visibly ageing. As compared with the condition

in youth or vigorous middle life,—

1. The fibrin of the blood and tissues is of a looser texture-i.e., less compactly organized.

2. The albumen is less perfect, forming a feebler coagulum when heated.

3. The chondrin (i.e., the condensed gelatin of the cartilages joining the ends of the bones in the joints) is less compact and dense; its spongy texture admitting nodules of earthy matter to be deposited in it.

4. The fat is more oily, softer, more fusible. 5. The bones are more brittle from a deficiency of the earthy phosphates. (See Note F, p. 157.)

6. The blood is weak, watery; its coagulum less in amount; its colour is darker; its saline constituents more variable; the total quantity circulating in the blood-vessels is less.

To these conditions of the proximate elements and component parts are referable the flabbiness of the muscles, wrinkled skin, sunken eyes, furrowed face, drooping features, stooping gait, diminished acuteness of the senses, dimness of vision, dulness of hearing, all more or less perceptible in advanced age.

That property of the textures in youth which we call resilience, springiness, elasticity, is lost in age. This fault in the lungs tends to the frequency of fatal congestion.

7. Nervine is the matter composing the brain, spinal chord and nerves. In the nerves, nervine, sheathed in a skin-like covering, is spread throughout the whole body. Where we can best see it, which is in the brain itself, we find it softer, yielding more readily to any slight violence, and visibly